The present invention pertains to microphones, and more particularly to a microphone associated with a vehicle accessory such as a rearview mirror assembly or the housing of a rear vision display device.
It has long been desired to provide improved microphone performance in devices such as communication devices and voice recognition devices that operate under a variety of different ambient noise conditions. Communication devices supporting hands-free operation permit the user to communicate through a microphone of a device that is not held by the user. Because of the distance between the user and the microphone, these microphones often detect undesirable noise in addition to the user""s speech. The noise is difficult to attenuate. A particularly challenging hands-free application where dynamically varying ambient noise is present is a hands-free communication system for a vehicle. For example, bi-directional communication systems such as two-way radios, cellular telephones, satellite phones, and the like, are used in vehicles, such as automobiles, trains, airplanes and boats. For a variety of reasons, it is preferable for the communication devices of these systems to operate hands-free, such that the user need not hold the device while talking, even in the presence of high ambient noise levels subject to wide dynamic fluctuations.
Bi-directional communication systems include an audio speaker and a microphone. In order to improve hands-free performance in a vehicle communication system, a microphone is typically mounted near the driver""s head. For example, a microphone is commonly attached to the vehicle visor or headliner using a fastener such as a clip, adhesive, hook and loop fastening tape (such as VELCRO(copyright) brand fastener), or the like. The audio speaker associated with the communication system is preferably positioned remote from the microphone to assist in minimizing feedback from the audio speaker to the microphone. It is common, for example, for the audio speaker to be located in a vehicle adaptor, such as a hang-up cup or a cigarette lighter plug used to provide energizing power from the vehicle electrical system to the communication device. Thus, although the communication system designer knows the position of the audio speaker in advance, the position of the microphone is unknown as the user can position the microphone where they choose. The position of the microphone relative to the person speaking will determine the level of the speech signal output by the microphone and may affect the signal-to-noise ratio. The position of the microphone relative to the audio speaker will impact on feedback between the speaker and microphone. Accordingly, the performance of the audio system is subject to the user""s installation of the microphone. Additionally, the microphone will typically include a wire, which if it is mounted to the surface of the vehicle interior, will not be aesthetically pleasing. Alternatively, if the wire is to be mounted behind the interior lining, the vehicle interior must be disassembled and then reattached so that the wire can be hidden, which may result in parts that rattle loudly or hang loosely from the vehicle frame.
One potential solution-to avoid these difficulties is disclosed in U.S. Pat. No. 4,930,742, entitled xe2x80x9cREARVIEW MIRROR AND ACCESSORY MOUNT FOR VEHICLESxe2x80x9d, issued to Schofield et al. on Jun. 5, 1990, which uses a microphone in a mirror mounting support. Although locating the microphone in the mirror support provides the system designer with a microphone location that is known in advance, and avoids the problems associated with mounting the microphone after the vehicle is manufactured, there are a number of disadvantages to such an arrangement. Because the mirror is positioned between the microphone and the person speaking into the microphone, a direct unobstructed path from the user to the microphone is precluded. Additionally, the location of the microphone on the windshield detrimentally impacts on microphone design flexibility and overall noise performance of the microphone.
U.S. Pat. Nos. 5,940,503, 6,026,162, 5,566,224, 5,878,353, and D 402,905 disclose rearview mirror assemblies with a microphone mounted in the bezel of the mirror. None of these patents, however, discloses the use of acoustic ports facing multiple directions nor do they disclose microphone assemblies utilizing more than one microphone transducer. The disclosed microphone assemblies do not incorporate sufficient noise suppression components to provide output signals with relatively high signal-to-noise ratios, and do not provide a microphone having a directional sensitivity pattern or a main lobe directed forward of the housing and attenuating signals originating from the sides of the housing.
It is highly desirable to provide voice recognition systems in association with vehicle communication systems, and most preferably, such a system would enable hands-free operation. Hands-free operation of a device used in a voice recognition system is a particularly challenging application for microphones, as the accuracy of a voice recognition system is dependent upon the quality of the electrical signal representing the user""s speech. Conventional hands-free microphones are not able to provide the consistency and predictability of microphone performance needed for such an application in a controlled environment such as an office, let alone in an uncontrolled environment such as an automobile.
Accordingly, there is a need for a microphone for a vehicle providing improved hands-free performance and preferably enabling voice recognition operation.
Historically, automotive microphones have. utilized a two wire interface to provide an audio signal from the microphone assembly to an electronic assembly (e.g., an amplifier stage). This two wire interface has also provided a power source to the microphone assembly and a wetting current through the interface such that reliable continuity was maintained between the microphone and the electronic assembly (see FIG. 35 and the description below).
Digital signal processors (DSPs) or other more advanced circuitry that may be used within a microphone assembly require more power than can normally be delivered through a standard two wire interface. As such, microphone assemblies incorporating DSPs may also require an auxiliary power source to be incorporated within the microphone assembly. However, implementing an auxiliary power source within a microphone assembly can introduce ground loops. Further, when non-precious metal contacts are used in a connector of a microphone interface, the contacts of the interface are prone to oxidation, which eventually leads to a continuity problem between the microphone assembly and the electronic assembly.
Thus, what is needed is a microphone interface for automotive microphone assemblies that include a power source that provides reliable continuity.
An aspect of the present invention is to provide a vehicle accessory having superior speech separation in the presence of noise. Another aspect of the present invention is to provide a vehicle accessory with enhanced performance for use in hands-free devices, including highly sensitive applications such as voice recognition for a vehicle telecommunication system.
To achieve these and other aspects and advantages, the vehicle accessory of the present invention comprises a housing; at least one transducer functioning as a microphone, the at least one transducer positioned in the housing; and a circuit coupled to the transducer for outputting an electrical signal such that the microphone has a main lobe directed forward of the housing and attenuating signals originating from the sides of the housing.
According to another embodiment of the present invention, a rearview mirror assembly is provided for achieving the above and other aspects and advantages, which comprises a rearview mirror housing; a mirror positioned in the rearview mirror housing; a microphone housing mounted on the rearview mirror housing, the microphone housing having at least one front port and at least one rear port; and at least one transducer positioned in the microphone housing, the at least one transducer including openings ported to the at least one front port and at the at least one rear port such that the microphone has a directional sensitivity pattern.
Another embodiment of the inventive vehicle accessory comprises at least one first transducer; at least one second transducer, wherein the first and second transducers are positioned in spaced relation; and a circuit coupled to the first and second transducers for combining the output signal of the first and second transducers to produce an audio signal with a reduced noise component.
The vehicle accessory may include a housing in which the transducers are positioned. Additionally, the housing may be mounted on a vehicle rearview mirror assembly. According to one embodiment of the present invention, the housing includes a deflector disposed proximate the transducers to deflect airflow away from the transducers. The deflector or other part of the housing may optionally include a fine turbulence generator disposed on at least a portion of its surface to create fine turbulence in air flowing around the deflector. According to yet another embodiment, the housing has an acoustic port, and a windscreen sealed across the acoustic port. The windscreen may have hydrophobic properties to prevent water from penetrating the housing through the acoustic port. The windscreen preferably has an acoustic resistivity of at least about 1 acoustic xcexa9/cm2.
According to another embodiment, the vehicle accessory may include: a first housing having at least one acoustic port, wherein the first transducer is disposed in the first housing and acoustically coupled to the acoustic port of the first housing; a first windscreen disposed across the acoustic port of the first housing; a second housing having at least one acoustic port, wherein the second transducer is disposed in the second housing and acoustically coupled to the acoustic port of the second housing; and a second windscreen disposed across the acoustic port of the second housing. With this arrangement, the first and second windscreens may have different acoustic resistivity, and the acoustic ports of the first and second housings may be configured differently, to compensate for differences, or create differences, in the polar patterns of the transducers.
In one embodiment, the vehicle accessory further includes a circuit board having a hole sized to receive at least a portion of the first and second transducers, wherein the transducers are mounted within the hole in the circuit board such that a portion of the transducers extends below a bottom surface of the circuit board.
According to one embodiment of the invention, the first transducer is positioned in front of the second transducer to provide a second order microphone. According to another embodiment of the invention, the vehicle accessory may include a mechanical structure disposed between the transducers to increase the acoustic path length between the transducers. The circuit may be configured to subtract the signal from the at least one first transducer from the signal from the at least one second transducer.
In one embodiment, the vehicle accessory further includes a high pass filter for filtering out low frequency components of audio signal generated by the second transducer, and the combining circuit subtracts at least a portion of one audio signal from the other to generate an audio output signal.
According to another embodiment, the first transducer receives an audio signal including a speech signal and noise, and generates a first electrical signal representative of the received audio signal, while the second transducer receives an audio signal including noise, and generates a second electrical signal representative of the received audio signal. The vehicle accessory may further include a speech detector coupled to the first and second transducers for detecting the presence of speech; a variable gain amplifier coupled to the second transducer for selectively adjusting the gain of the second electrical signal in response to a gain adjustment signal; and a control circuit coupled to the first and second transducers, the speech detector, and the variable gain amplifier for generating the gain adjustment signal as a function of the levels of the first and second electrical signals received from the transducers and in response to a detection of speech by the speech detector.
Another aspect of the present invention is to provide an audio system having superior speech separation in the presence of noise. Another aspect of the present invention is to provide an audio system with enhanced performance for use in hands-free devices, including highly sensitive applications such as voice recognition for a telecommunication system.
To achieve these and other aspects and advantages, the audio system of the present invention comprises a microphone for receiving an audio signal including a speech signal and noise, and for generating an electrical signal representative of the received audio signal, and a filter coupled to the microphone for receiving the electrical signal generated by the microphone and filtering the electrical signal to significantly reduce the noise and produce a filtered electrical signal including the received speech signal. The filter includes a plurality of narrow passbands at frequencies spaced from each other by a predetermined frequency corresponding to a fundamental frequency in the speech signal. The filter thereby blocks frequency components of the received audio signal that lie between the plurality of narrow passbands.
According to another embodiment of the present invention, an adaptive filter is provided for removing noise from an audio signal including a speech component signal. The adaptive filter of the present invention comprises a digital signal processor configured to: convert a received analog signal into a digitized audio signal; identify a fundamental frequency and harmonics in the speech component of the digitized audio signal; provide an inverse comb filter; and pass the digitized audio signal through the inverse comb filter to filter out frequency components of the digitized audio signal that do not correspond to the identified harmonic frequencies. The digital signal processor may further be configured to convert the filtered digitized audio signal into an analog signal for output from the digital signal processor. The digital signal processor identifies the fundamental frequency by (a) performing a fast Fourier transform on the received audio signal, (b) identifying frequency components in the fast Fourier transform that have amplitudes exceeding a predetermined threshold, and (c) identifying the fundamental frequency as the difference in frequency of those frequency components having an amplitude above the predetermined threshold.
The present invention is also directed to a technique for providing reliable continuity through a two wire microphone interface that removably couples a microphone to an electronic assembly. The microphone includes a power source and the two wire microphone interface, which includes two contacts that provide an audio signal to the electronic assembly. A continuous direct current is provided through the two contacts such that a low impedance path is maintained between the microphone and the electronic assembly.